1. Field of the Invention
The present invention relates generally to electronics modules and specifically to a module assembly incorporating a printed circuit board and a pallet. The invention further relates to methods of manufacture of such electronics modules.
2. Description of Related Art
Electronics modules for relatively high power applications, such as RF power amplifiers, typically include one or more printed circuit boards (PCBs) and/or discrete electronic components coupled to a metallic pallet. The pallet provides electrical grounding and transfer of heat generated by the PCB and various electronic components. In a conventional electronics module assembly, the printed circuit board is mounted to the pallet by means of fasteners, such as bolts. Since the sizes of pallets and printed circuit boards tend to be small, the use of bolts occupy a substantial amount of space relative to the area of the printed circuit board. As a result, the printed circuit board has less room for electronic components, such as RF transistors.
Furthermore, a bolted connection does not provide a substantially uniform connection between the printed circuit board and the pallet. As a result, thermal transfer to the pallet may be uneven and less efficient overall. This reduces the lifetime of the electronics in the assembly. Another approach to mounting the module to the pallet employs bonding the module to the pallet. This approach also provides uneven thermal connection to the pallet. Also, an assembly may become loose over time as the PCB moves away from the pallet, leading to loss of necessary grounding and heat diffusion. Assemblies employing fasteners are also vulnerable to separation caused by temperature cycling, which occurs frequently in RF applications.
What is needed, therefore, is a more reliable electrical and thermal connection for electronics modules which will not degrade over time and temperature cycling. What is further needed is a process for assembling electronics modules and pallets that provides greater manufacturability.
The present invention provides structures and methods which overcome the deficiencies in the prior art.
In one aspect, a durable, electronics module assembly with a conductive preform layer is provided. The first preferred embodiment includes a bottom pallet having recesses conforming to the underside traces of the PCB layer. The top surface of the pallet is plated with gold. Solder mask is applied to the top surface for directing the placement of electronic components. The conductive preform layer includes trace apertures conforming to the underside traces of the PCB layer. Spacing is provided in the preform layer for receiving electronic components. The conductive preform layer is sandwiched between the bottom pallet and a top printed circuit board layer. The bottom surface includes conductive traces and a protruding waffle pattern for providing better adhesion to the preform.
In a further aspect, a method for manufacturing the first embodiment is provided which includes a laminating process. The laminating process comprises placing the pallet, epoxy preform layer and PCB in a laminating fixture, thus forming a pre-cured sub-assembly. The preform layer is cured by simultaneously heating the sub-assembly while applying pressure. The fixture is placed within an oven at a predetermined temperature and within a press that applies a predetermined pressure to the sub-assembly via a press pad. In a preferred embodiment wherein thermal set epoxy is employed, the preform may be cured by applying pressure to the sub-assembly while maintaining the sub-assembly at or above the thermal set temperature of the epoxy. The cured sub-assembly may be cooled by inserting the laminating fixture into a cold press. Pressure should still be applied to sub-assembly as it is cooled. The cured sub-assembly is removed from the fixture and any excess epoxy resin in the component wells is removed. The cured sub-assembly is examined for any delamination to ensure that a seal is formed around the border of the entire structure.
In another aspect, an electronics module assembly with a primarily non-conductive preform layer is provided. Unlike the first preferred embodiment, this alternate embodiment comprises a non-conductive preform layer with traces of conductive epoxy disposed thereon. The conductive epoxy traces provide grounding of the PCB layer and certain RF electrical components included within the assembly. This embodiment of the invention may be preferred in some applications.
A method is also provided for manufacturing the electronics module assembly with the primarily non-conductive preform layer. This method for fabricating the second preferred embodiment also includes the lamination process according to the invention.
In a further aspect, an RF power amplifier assembly according to the invention comprises a housing, a circuit including an input signal to be amplified and an output signal, and an electronics module assembly including a printed circuit board layer, an epoxy preform layer, and a pallet.
It will be appreciated that the above summarized methods of assembly and manufacture can provide a high performance electronics module assembly with excellent thermal and electrical connection due to the lamination of the PCB layer to the pallet with the epoxy preform layer. The assembly is resistant to delamination or other degradation over time despite thermal cycling. It will also be appreciated that the methods provided lead to greater ease of automation and lower cost in manufacturing.
The invention, now having been briefly summarized, may be better appreciated by the following detailed description.